Conductive elements, such as capacitive sensing elements and conductive tracks, are increasingly being incorporated into printed articles, such as books, posters and greeting cards, to allow printed articles to become interactive. Examples of interactive printed articles are described in GB 2 464 537 A, WO 2004 077286 A, WO 2007 035115 A and DE 1993 4312672 A.
Such interactive printed articles can suffer one or more drawbacks.
Capacitive sensing elements can be formed using conductive inks containing particles or flakes of carbon or a metal, such as silver. Metal-based inks tend to have better electrical properties than carbon-based inks. However, metal-based inks are generally more expensive and can be more damaging to the environment than carbon-based inks.
Conductive tracks, usually formed from conducting ink, are used to connect the capacitive sensing elements to terminals. If a wide track is used, then the track may have a sufficiently large capacitance to serve as a capacitive sensing element. Thus, proximity of a user's finger to the track may unintentionally trigger a response. One solution is to reduce the width of the track and, thus, its capacitance. However, this has the effect of increasing the resistance of the track thereby reducing the maximum frequency of operation. Normally, if the width of the track is reduced, then a shorter track is used. The use of a narrower track also increases the chances that a broken track is formed during manufacture due to a defect, for example, a print defect, or that a working track is broken when handled or processed.